BENGHAZI, Libya (CBS) -- The U.S. Ambassador to Libya and three other Americans were killed during an attack in Benghazi, Libya. President Obama and Secretary and State Hillary Clinton are condemning the attack and pledging that those responsible will be brought to justice.

Chris Stevens, the U.S. ambassador to Libya, was killed as the American consulate came under attack in Benghazi. U.S. officials confirm Stevens, information officer Sean Smith and two other Americans were killed as they tried to evacuate staff members. President Obama says, "There is absolutely no justification for this kind on senseless violence."

Gunman armed with automatic weapons stormed the consulate overnight, overwhelming Libyan security forces and setting the building on fire. Secretary of State Hillary Clinton says, "This is an attack that should shock people of all faiths around the world."

At the President's order, there is now increased security at U.S. diplomatic stations around the world. Americans in countries bordering Libya are being warned to avoid crowded places.

Stevens was a career diplomat who had already served two tours in Libya. Clinton says, "He risked his life to stop a tyrant and gave his life to help build a better Libya."

The unrest started in Cairo, Egypt where demonstrators scaled the wall of the U.S. embassy and tore down the American flag.

Republican White House hopeful Mitt Romney accused the Obama Administration of sending mixed signals about condemning the attack. Romney said, "I believe the administration was wrong to stand by a statement, sympathizing with those who had breached our embassy in Egypt, instead of condemning their actions."

A U.S. official says the bodies of the four Americans have been taken to Tripoli. Stevens was the first U.S. ambassador to be killed in the line of duty since 1979.